1. Field of the Invention
The present invention relates to a work-supporting deck for use with machine tools, particularly cutting machines for cutting flat stock. The deck comprises a large number of vacuum aspirators that have lifting rams supporting suction cups, which serve to support and retain a workpiece. The lifting rams are vertically displaceable by actuators and may be fixed in position by a clamping device.
2. The Prior Art
Work-supporting decks having a work-supporting surface, at which a vacuum can be applied, have proved satisfactory for use in the processing of flat stock, such as the trimming or contour milling of metal plates and parts of wood, and particularly of monolayer plastic blanks or multilayer plastic blanks (composites). The two-dimensional workpieces can reliably be retained on the work-supporting surface by the applied vacuum substantially independently of their geometric configuration. But in order to avoid damage to such so-called vacuum decks, they must be provided with cover plates which support the workpieces and consist of an air-permeable material or of contour templates provided with suitable gaskets. But contour templates involve a substantial expenditure and must conform to specific workpieces so that their use is restricted. The porous cover plates of foamed plastic also are not satisfactory because furrows will be cut into the cover plate as it is penetrated by the tool during its processing operation and such furrows will adversely affect the application and action of the required vacuum. For this reason it is necessary to use a tool which laterally protrudes over the workpiece to the smallest extent possible and to cover the workpiece at its edges with plastic films so that the utilization of the tool is decreased and the films must be handled in a complicated manner.
In EP-8 0069 230 it has already been suggested to provide a work-supporting deck with several vacuum aspirators and to support the workpieces only by the suction cups of said aspirators rather than on a continuous work-supporting surface. But the workpiece cannot be retained as desired by the known vacuum aspirators unless they engage the workpiece at predetermined points so that each aspirator must individually be laterally adjusted and the work-supporting decks provided with said aspirators can be used only to support workpieces having a predetermined shape. Besides, the workpiece is supported only at a few points so that the processing of the workpiece gives rise to vibration, which often preclude the use of mechanical means for additionally fixing the workpiece.
An attempt to overcome certain of these drawbacks has resulted in work-supporting decks with adjustable vacuum aspirators for cutting spatially preshaped, thin-walled workpieces, or workpieces having a curved surface. These vacuum aspirators can be adapted to the particular workpieces on account of their vertically adjustable lifting rams, and the elastic properties of the aspirator material or of an articulated support of the suction cups. These decks are capable of holding workpieces with a complicated and delicate shape with the strength and stability sufficient for processing the workpiece effectively.
As shown by U.S. Pat. No. 4,684,113, it is known to drive the individual lifting rams by computer-control up into the particular nominal position in accordance with the surface of the workpiece, and to fix them in the nominal position via a clamping device. This, however, requires a positionable actuator for each vacuum aspirator and consequently leads to high construction and control expenditures.
According to GB-A 22 05 258, it has also already been proposed to use a tool-driving unit associated with the work-supporting deck for positioning the vacuum aspirators. The tool-driving unit is equipped with a workpiece spindle or the like that can be controlled in the z-direction and can preset the exact vertical position for the particular vacuum aspirator. For positioning the vacuum aspirators, only the workpiece spindle needs to be raised above the particular aspirator to the corresponding nominal level. The lifting ram of the vacuum aspirator is then driven up to the adjusted workpiece spindle until reaching the stop, so that said vacuum aspirators can be adjusted without costly positionable actuators and fixed in the adjusted position with a suitable clamping device. However, placing a workpiece on a large number of positioned vacuum aspirators posed considerable problems heretofore because when the workpiece is placed on the suction cups, the individual suction cups first have to be swivelled into the angular position that is correct for properly attaching them to the surface of the workpiece. This, however, is frequently not successfully accomplished because the suction cups attach themselves by suction too quickly to the surface of the workpiece, resulting in a faulty support. If the additional expenditure of individual connections of the vacuum aspirators with a vacuum source is avoided and the vacuum aspirators are automatically connected with a vacuum source, usually simultaneously with the raising into their nominal positions, there is consequently the risk that the workpiece is supported without the desired exactness, and the cutting of easily deformable, thin-walled workpieces is not feasible at all.
Furthermore, a work-supporting deck is known from EP-A 0 505 668, where the vacuum aspirators can be raised individually and in two performance stages. Therefore, it is possible in this case to first raise a few of the aspirators into their final positions, for example, the aspirators disposed in the marginal zone of the workpieces, as support points for a workpiece to be treated, and to then place the workpiece on these fixed support points. A few aspirators can still correctly attach themselves to the workpiece and fasten themselves on the latter by suction. Thereafter, all the other aspirators that are to be attached to the inner zone of the workpiece, are raised until they come to rest against the already positioned workpiece and perform their support function. In this connection, the vacuum aspirators rising to attach on the workpiece are forced up with a lower force in order not to impair the positioning support of the workpieces when they attach themselves. However, such later attachment of the majority of aspirators requires a sufficiently rigid workpiece, which through its dimensional stability jointly determines also the nominal positions of the aspirators. These work-supporting decks are unsuitable for delicate workpieces with a flexible soft surface.
Therefore, the invention based on the problem of eliminating such drawbacks and to create a work-supporting deck of the type specified above that assures in a relatively simple way and with low expenditure a flawless and careful supporting and cutting of any type of workpiece, including delicate workpieces.